1. Field of the Invention
This invention relates to a sheet material conveying apparatus, and particularly to a sheet material conveying apparatus for supplying sheet materials placed, for example, on a supporting portion one by one to an image processing position, and image-processing one surface or both surfaces of the sheet material, and thereafter conveying the sheet material to a discharging portion. Specifically, it relates to a sheet original conveying apparatus attached to an image processing apparatus such as a copying apparatus, a facsimile apparatus, a scanner or a printer.
2. Related Background Art
Conventionally, a sheet material conveying apparatus attached to an image processing apparatus such as a copying apparatus, a facsimile apparatus, a scanner or a printer has heretofore been designed to supply sheet materials placed on a supporting portion one by one to an image processing position, and image-process one surface or both surfaces of the sheet material, and thereafter convey the sheet material to a discharging portion.
A case where the image processing is the process of reading the image of an original will hereinafter be shown by way of example and described.
Of original reading apparatuses provided with the conveying apparatus, as an apparatus coping with an original having images to be read on the front and back surfaces thereof, there is well known an apparatus capable of first effecting the reading of the image of the front surface of the original, and then automatically reversing the original surfaces in an original feeding apparatus and re-supplying the reversed original to the original reading position to effect the reading of the image of the back surface of the original.
Also, in a digital image processing apparatus wherein the reading and memory preservation or the like of image data are combined together, it has become more important than before to increase the number of sheet materials such as originals processed per unit time from the necessity of reading or processing images within a copying time. For that purpose, it is necessary to make the interval between originals (original interval) small and minimize the afore described time for reversing the original surface.
With this as the background, a case where not so-called switch back reversal but reversal using a U-turn conveying path is adopted for the reversal of the original because of the ease of the mirror image processing of images accumulated in a memory by digitization has increased.
Further, in the U-turn reversing process in such a digital image processing apparatus, the following control becomes possible making the most of the merit that the free processing of image signals accumulated in the memory is possible. It is the control that only the images of the front surfaces of a predetermined number of originals are collectively read in, then the originals are successively subjected to U-turn reversing process, and then the images of the back surfaces of the originals are likewise collectively read in. By effecting such control, the processing speed is improved as compared with a case where the images of the front and back surfaces of each original are read in.
In the above-described example of the prior art, however, the originals supported on a supporting portion (tray) are first supplied one by one to an image reading position via a pay-away portion and a separating portion, and therefore there may sometimes occur some delay of the feeding time in the pay-away and separation of the originals. This delay of the feeding time results in an increase in the sheet interval. Thus, when considering a case where as previously described, a predetermined number of originals are collectively image-processed, the full length of the ranging originals is also increased by such an increase in the sheet interval.
On the other hand, since the predetermined number of originals are collectively contained in the path and reversal-processed, the length of a reversing path is determined in conformity with the full length of the predetermined number of originals contained.
These facts have led to the problem that when the feed timing of the original is delayed in the manner described above, the sheet interval increases, so that the full length of the ranging originals increases and a predetermined number of originals become incapable of being contained in the reversing path.
As means for solving such a problem, there is known an example using control as will be described below. When the sheet interval increases in the manner described above and a predetermined number of originals become incapable of being contained in the reversing path, the number of originals to be contained in the reversing path is decreased and originals which could not be contained are caused to stand by on this side of the entrance to the reversing path and are processed.
An example of the processing in a reversing path capable of containing, for example, two sheets of A4 size originals is shown in FIGS. 14A to 14E of the accompanying drawings.
As shown in FIGS. 14A to 14E, there are two originals P.sub.1 and P.sub.2 originally contained in a reversing path 101 and to be collectively processed. Let it be assumed here that in FIG. 14A, a delay during sheet feeding has occurred to the second original P.sub.2. Neither of the two sheets can intactly be contained in the reversing path 101, and therefore in FIG. 14B, the second original P.sub.2 is caused to stand by on this side of the entrance to the reversing path 101. Then, in FIGS. 14B to 14D, the reversing process of the first original P.sub.1 is completed, then in FIG. 14E, the conveyance of the second original P.sub.2 into the reversing path 101 is started to effect the similar processing.
By using such control, the originals can be processed without colliding against each other.
However, taking the case described with reference to FIGS. 14A to 14E as an example, the two originals P.sub.1 and P.sub.2 which originally should have been collectively processed are processed one by one after all. And when a delay of sheet feeding occurs continuously, there arises the problem that the original processing speed (productivity) is reduced to about a half.